The present invention relates to a filter as an insert in a filter cup consisting of hollow cylindrical open-pore ceramic foam and an end plate of gas-impermeable material for cleaning exhaust gases of diesel engines, in which the exhaust gases flow through the active filter section essentially perpendicularly to the cylinder axis.
A filter of the aforementioned kind is known from European patent application 0 216 729.
The soot components of the exhaust gases of diesel engines can basically be reduced in two ways: by optimizing mixture preparation and the combustion process in the engine and by fitting filters in the exhaust stream. Depending on the design of the filter, usually degrees of soot precipitation of 50-90% are obtained.
The active filter volume cannot however be increased as desired to obtain optimum soot precipitation, for the filter acts as a resistance which generates a back pressure counter to the exhaust gas. The back pressure must not be too high, as otherwise the engine power is reduced and fuel consumption is increased. For example, in diesel engines which are used in motor vehicles for road use, particularly passenger cars, and which are fitted with exhaust filters, the back pressure should be not more than 0.2 bar.
On account of the size of the diesel engines for trucks and passenger service buses, particularly large exhaust filters are needed. In this case there is the problem that both larger ceramic foam components can be made from one piece only with increased requirements because the necessary dimensional accuracy necessitates increased expenditure and hence the economy of using ceramic foam is greatly impaired. In addition the back pressure increases considerably as with conventional structural measures as shown e.g. by U.S. Pat. No. 4 264 346, in which the exhaust gases impinge on the end face of a cylindrical ceramic foam piece and flow through it parallel to its axis (axially).